Idiopathic Pulmonary Fibrosis (IPF) is the most common form of Idiopathic Interstitial Pneumonia and is associated with a median survival of approximately 5 years from the time of diagnosis. Several medications may be used for this disease, including corticosteroids and other immunosuppressive agents, although their benefit is unclear. Further, these agents, particularly corticosteroids, have been associated with significant adverse effects, in other populations. Current guidelines are available to help guide clinicians, but it is not known if these guidelines are followed, which medications are most commonly used, or which factors impact the decision to initiate therapy at the time of diagnosis or the choice of agents prescribed. The broad, longterm objectives of this application are to address these areas of uncertainty and therefore better determine how treatment strategies could be refined to minimize the exposure of patients to the potential toxicities of existing therapy. The proposed cohort study will therefore focus on the following three specific aims: 1) Quantifying the use of corticosteroids and corticosteroid-sparing agents and the doses of medications prescribed to patients with IPF in broad-based clinical practice;2) Determining which disease and demographic factors are associated with the initiation of corticosteroid therapy at the time of diagnosis with IPF;and 3) Determining which disease and demographic factors are associated with the initiation.of combination therapy using corticosteroids and corticosteroid sparing agents compared to the use of corticosteroids alone. The proposed study will use a fully anonymized medical record research database from the United Kingdom to evaluate a cohort of approximately 2100 patients with IPF. This would be the largest study of its kind in this disease. From this database, a retrospective cohort study will be conducted and analyzed using bivariable and multivariable analyses to evaluate the association between patientspecific exposure variables and the use of corticosteroids or combination therapy. Relevance: This study aims to understand which factors influence physician decision-making in the treatment of Idiopathic Pulmonary Fibrosis, a progressive and fatal lung disease for which treatments are Often ineffective and associated with significant side effects. The results will lay the foundation for further research quantifying the risks of therapy and the ways in which these risks can be balanced more effectively against the marginal benefits of treatment.